This application relates to the field of electric machines, and more particularly, electric machines having bent conductor windings.
Electric machines are important components of conventional internal combustion engine automobiles. For example, electric machines typically serve as starting motors to crank automobile engines. Other electric machines serve as alternators that generate electricity from engine motion and deliver power to automobile loads. Electric machines are also very important in modern hybrid electric vehicles (HEVs), serving as a core component in the HEV's electric drive system.
The electric machine in many HEVs comprises a laminated stator stack with a plurality of rectangular windings inserted into the stator slots. In order to insert the windings into the stator slots, U-shaped segmented conductors (also referred to herein as “hairpins” or “U-shaped bars”) of rectangular cross-section are utilized. These hairpins are created by cutting a rectangular conductor into many segments with each segment having a certain length. The straight segments of wire are then bent and twisted into U-shaped conductors (or “hairpin” conductors) with the proper span for the electric machine. Next, the U-shaped conductors are inserted into the slots of the stator core from an insertion end of the stator. After the U-shaped conductors are inserted into the slots, the legs of the hairpin conductors extend from a connection end of the stator in multiple radial rows of conductors. These leg ends are then bent to appropriate positions before connections are made between the conductors. FIG. 7 shows a plurality of bent conductors 12 provided in an outer row of conductors for an exemplary stator core 14. An exemplary four layer conductor arrangement is disclosed in U.S. Pat. No. 7,034,428 to Cai et al., the contents of which are incorporated herein by reference.
Precise bending (also referred to herein as “twisting”) of the leg ends of the U-shaped conductors facilitates proper connections between the conductors. However, it can be difficult to bend the conductor ends the exact amount required for a proper connection. In particular, there is relatively little space between the conductors at the end of the stator, and this alone makes access to the conductors and any associated movement required for bending of the conductors difficult. Furthermore, the metal conductors are resilient and tend to spring back to some extent toward their original position after they are bent. This makes precise bending to a desired degree or to a desired location difficult. Furthermore, when a conductor is bent, the height profile of the conductor is changed. In particular, the greater the degree of bending required, the lower the final height profile of the bent conductor. With current bending machines, the rotation and height positioning are not independent. An inability to adapt to the changing height of the conductor during bending may result in an improper bend.
In view of the foregoing, it would be advantageous to provide a method and device for twisting stator windings in a more precise fashion. It would also be advantageous if such twisting could be done quickly and with relative ease. It would also be advantageous if such twisting could be accomplished while adapting the system to accommodate for both the rotational offset and the height change in the conductors during the twisting process.